Electroanalysis of melatonin using castor oil–graphite paste electrode

A carbon paste electrode containing castor oil as a binder was prepared and the preconcentration of melatonin at this electrode was examined. Melatonin proved to be readily extracted into castor oil, thus allowing its sensitive determination by extractive stripping voltammetry. The response was evaluated with respect to pH, preconcentration time, reproducibility and other variables. Under optimal conditions, a detection limit of 1 × 10–9 mol dm–3 was obtained and the calibration curve was linear over the range 5 × 10–8–1 × 10–7 mol dm–3. Applying the medium-exchange approach enhanced the selectivity of determination. A simple procedure was developed for the voltammetric determination of melatonin in serum samples.